The present invention relates to a resistor that is incorporated in a cathode-ray tube (hereinafter referred to as a CRT inner resistor or an inner resistor) and, more particularly, to a CRT inner resistor capable of preventing leak current.
A CRT inner resistor for supplying a prescribed focus voltage and convergence correction voltage is provided in the electron gun portion of a CRT. As shown in FIG. 1A, an inner resistor 6 as mentioned above has an insulating substrate 11, and electrodes 12a-12c and a resistive body 13 that are provided on the insulating substrate 11. The electrodes 12a-12c are provided in series at both ends and a prescribed intermediate position of the resistive body 13. As shown in FIG. 1B, an insulating glass layer 14 is provided on the insulating substrate 11 so as to cover the resistive body 13. The insulating glass layer 14 is to protect the resistive body 13 from the high-voltage environment inside a CRT.
With the inner resistor 6, a prescribed intermediate voltage can be obtained from the electrode 12c that is provided at the prescribed intermediate position of the resistive body 13 by using, as a ground side, the electrode 12a that is connected to one end of the resistive body 13 and supplying a high voltage to the electrode 12b that is connected to the other end of the resistive body 13.
However, the inner resistor having the above structure has the following problems.
In the inside space of a CRT where the inner resistor is disposed, scanning with electron beams is performed by supplying a high voltage of about 20-30 kV. Therefore, stray electrons slightly exist in the vicinity of the inner resistor and cause charging of the surface of the insulating substrate.
However, as shown in FIGS. 2A (enlarged view of the main part) and 2B (sectional view of the main part), the peripheral portions of the respective electrodes 12a-12c (represented by the electrode 12c in those figures) of the inner resistor 6 have what is called a "knife edge" shape in which the film thickness gradually decreases from the central side to the outside because the electrodes 12a-12c are formed on the insulating substrate 11 by screen printing. Therefore, as shown in FIG. 2C, which is an enlarged view of part B of FIG. 2B, an electric field is concentrated in the vicinity of the circumference of the electrode 12c owing to slight charging of the surface of the insulating substrate 11 and the electric field strength is increased there. Electrons are emitted from the circumferential portion of the electrode 12c by field emission and leak current occurs. As a result, the potential of the electrode 12c is varied.
This is a factor of causing problems of mis-focusing due to a variation in focus voltage and a mis-convergence due to a variation in convergence correction voltage.